It didn't consider the case of the incoming size not allowing for the
2*data_size range for t_buf->{prod,cons}

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- 2010-06-15.orig/xen/common/trace.c	2010-06-28 11:58:37.000000000 +0200
+++ 2010-06-15/xen/common/trace.c	2010-06-28 11:58:37.000000000 +0200
@@ -77,11 +77,16 @@ static u32 tb_event_mask = TRC_ALL;
 
 /**
  * check_tbuf_size - check to make sure that the proposed size will fit
- * in the currently sized struct t_info.
+ * in the currently sized struct t_info and allows prod and cons to
+ * reach double the value without overflow.
  */
-static inline int check_tbuf_size(int size)
+static int check_tbuf_size(u32 pages)
 {
-    return (num_online_cpus() * size + T_INFO_FIRST_OFFSET) > (T_INFO_SIZE / sizeof(uint32_t));
+    u32 size = pages * PAGE_SIZE;
+
+    return (size / PAGE_SIZE != pages) || (size + size < size) ||
+           (num_online_cpus() * pages + T_INFO_FIRST_OFFSET >
+            T_INFO_SIZE / sizeof(uint32_t));
 }
 
 /**